This invention relates to a chip bonding apparatus for bonding a chip such as a semiconductor device on a substrate, and more particularly to a support structure for supporting a tool (hereinafter called xe2x80x9cheadxe2x80x9d) that holds the chip and press-fits it on the substrate.
As one of typical techniques for installing a chip directly on a substrate, the ACF (Anisotropic Conductive Film) technique is known. This technique uses ACF having conductive particles mixed into an adhesive to secure the chip on the substrate. The chip is installed on the ACF applied to the substrate, thereby bonding the chip to the substrate, and at the same time electrically connecting the chip and substrate by the conductive particles placed between upper and lower electrodes. In the ACF technique, a polyester film coated with an adhesive is supplied from an ACF tape feeder, and, while peeling off a separator, the adhesive layer is scored, and heated and pressed by a heat tool from above, whereby the ACF is transferred to the substrate. Next, when the chip held by the head is press-fitted to the ACF from above, bumps of the chip and electrodes of the substrate become conductive through the conductive particles in the adhesive. The chip is heated and pressurized in time of press-fitting, whereby the adhesive (binder) cures to bond the chip and substrate in a conductive state.
A conventional chip bonding apparatus used in a process of press-fitting a chip on a substrate will be described hereinafter with reference to the drawings. FIG. 1 shows an outline of a conventional chip bonding apparatus.
The conventional chip bonding apparatus has a pressure cylinder 3 attached to an inversed L-shape head mounting post 15 for pressing a head 1 holding a chip toward a substrate 2. The pressure cylinder 3 has a rod 3a supported in an intermediate portion thereof by the head mounting post 15 through a slide unit 16. The head 1 is attached to the lower end of the rod 3a of the pressure cylinder 3. There is a table 6 below the head 1. The table 6 holds thereon the substrate 2 which has ACF transferred thereto. The chip, not shown, is held on the lower surface of the head 1. The rod 3a of pressure cylinder 3 is extendible in this state to press-fit the chip on the substrate 2.
In the conventional chip bonding apparatus, as noted above, the pressure cylinder 3, slide unit 16 and head 1 are integrated with the head mounting post 15. When the head 1 presses the chip on the substrate 2, a reaction thereof pushes up a horizontal portion of the head mounting post 15 supporting the pressure cylinder 3 to apply a bending moment to the head mounting post 15, to bend or warp the head mounting post 15. This results in a deviation or error in parallelism in the order of several microns occurring between the head 1 and table 6.
The deviation or error in parallelism between the head 1 and table 6 causes the following inconvenience. That is, as shown in FIG. 2, a bump 23 on the chip 22 and an electrode 24 on the substrate 2 opposed to each other across a conductive particle 21 in the ACF rub against each other (i.e. shift in a horizontal plane relative to each other). This causes the conductive particle 21 between the bump 23 and electrode 24 to roll though slightly, thereby to create an oval spread space between the bump 23 and electrode 24. As a result, the area of contact between the conductive particle 21 and bump 23 or the conductive particle 21 and electrode 24 diminishes to increase conduction resistance or cause variations thereof. As a solution to this, it is conceivable to increase rigidity of the head mounting post 15, but there is a limitation.
Particularly, as a recent tendency, from a viewpoint such as of shortening the processing time of a press-fitting step, apparatus have been proposed and implemented to press-fit chips simultaneously by using two or more heads. In such a multi-head apparatus, the above problem becomes even more prominent.
The present invention has been made having regard to the state of the art noted above, and its object is to prevent a deviation or error in parallelism occurring with a head when press-fitting a chip.
The present invention provides a chip bonding apparatus for press-fitting a chip on a substrate, characterized by comprising a head for holding the chip, a pressure cylinder for pressing said head toward the substrate, a first support mechanism for supporting said pressure cylinder to be movable up and down, and a second support mechanism separate from and independent of said first support mechanism for supporting a reactive force acting on said pressure cylinder when said head is pressed toward the substrate.
According to the present invention, since the pressure cylinder is supported by the first support mechanism to be movable up and down, when a reactive force acts on the pressure cylinder in time of chip press-fitting, the reactive force is borne by the second support mechanism. Since this second support mechanism is separate from and independent of the first support mechanism, even when the second support mechanism bends or warps under said reactive force, its influence is not transmitted to the first support mechanism. That is, since the first support mechanism supporting the pressure cylinder does not bend or warp, the head is free from a deviation or error in parallelism in time of press-fitting.
Preferably, the second support mechanism supports the reactive force acting on the pressure cylinder, by contacting the pressure cylinder. With this construction, since not only the first support mechanism but also the pressure cylinder is free from the influence of the bending or warping of the second support mechanism, the deviation or error in parallelism of the head may be further suppressed in time of press-fitting.
The contact structure between the second support mechanism and pressure cylinder may be either direct contact or indirect contact. From the viewpoint of reducing frictional resistance, the contact structure, preferably, is a point contact such as a spherical point of contact, for example.
The present invention is applicable to both an apparatus having one set of head and pressure cylinder, and an apparatus having plural sets of head and pressure cylinder. In the apparatus having plural sets of head and pressure cylinder also, the first support mechanism for supporting each pressure cylinder to be movable up and down and the second support mechanism for supporting a reactive force acting on each pressure cylinder are constructed separate from and independent of each other.